Roasting-furnace.



F. LAIST. ROASTING FURNAOE. APPLIGATION FILED 20.23. 1912.

Patented Aug. 19, 1933.

SHEETS-SHEET l.

uw- 'ab 05255320: 0-03 1:

IMVIENTOR. Frama/f amb WITNESSES:

@ ATTORNEY.

F. LAIST. RoAs'rING FURNAOB." APPLIOATIQM Hmm-,masi 1912.

Patented Aug. 1.9, 19W,

4 SHEETS-SHEET 2.

I INYENTOQ. t WM5/edf im@ WITNESSES.-

A 'FTORNE Y.

1?, MIST. ROASTING EURNAGIJ.

APPLIOAToN FILED DBO. 23. 1912.

Patented Aug. 19, 11913.

L SHEETS-SHEET 3.

LYAQ@ lA TTORNEY.-

FREDERICK LAIST, 0F ANACONDA, MONTANA.

RoAsTmG-FURNAGE.

1,07 (MMM).

Application filed December 23, 1912.

To frH fir/1 ont M12/ay concern Be it known that I, FREDERICK LixIsT, a citizen of the United States. residing at Anaconda, in the county of Deerlodge and State of Montana, have invented certain new and useful lmprovemcnts in Roasting- Furnaces. of which the following is a full, clear, and exact description, reference being had to the accompanying` drawings, forming a part hereof.

My invention has relation to 'improvements in roasting' furnaces; and it consists in the novel details of construction more fully set forth in the specification and pointed out inthe claims. v

ln'the drawings. Figure l is a combined elevation and middle vertical sect-ion of the furnace. the section being taken through one of the lire-boxes: Fig. Q is a top plan. parts bein;y broken away: Fig. 2l is an enlarged vertical sectional detail of the upper 'hearth or lloor. with parts otl the ore-feed mechanism in elevation: File'. -t is a horizontal section on'lhe line l---Jf of Fig'. l taken above the iabbl -\-arins in the directtired hearth.'

parts being broken away: Fig". 5 is an enlarged vertical section on the curved line 5*-5 of Fig. l showing' the detailed construction of the feed-hopper leading from the third to the fourth hearth: Fig". is a combined elevational and sectional detail showing theI rabble-shaft and the sand-seal which is interposed between the third and.

fourth hearths; and Fie. T- is a diagrammatic plan showing' the relative position ot' the drop hol-es leading` from the second to the third hearth. and the discharge openinpjs from'the lire-boxv leading' into the third hearth. l

The present invention is directedrto nnprovcments in a type of roasting/furnacel known as the McDougal, the objects in view beine' to malte this type serviceable for Specification of Letters Patent.

Patented Aue'. MD, it?.

serial No. 738,249.

be almost entirely overcome; one in which the chloridation may be effected without the application of external heat. the. heat of the calcines delivered from the roasting' hearths to the chloridizingh hearths being' suiiicient for that purpose; one in which overheatinf.,r of the charge 1s prevented, thereby avoiding the formation of compounds (no` tably ferrite copper) which are insoluble in the leaching solution; one which shall be scription of the invention which is as follows:

Referrrinpto the drawings. F represents the furnace (extending partly above and partly below the ioor-line L), and a, b, c, (l. e. f'. the several superimposed hearths in which the material' is treated (the Dres-ent being a six-hearth multiple-liearth furnace). the material dropping from .the upper hearths successively through the'several hearths until itis delivered into the discharjie hopper C. the hearths being provided with the central and marginal openings or drop-holes o. 0'. for the passage of the material. Passingy centrally through the hearths is the rotatable hollow rabble-shaftl from which radiate the Series of hollow rabble or stirrer arms 2 extending` into the several hearths and carryingr altes 3, by which the material is successively fed from one hearth to the hearth immediately beneath it, the shaft and arms beineprovided witlrwatercirculating cooling pipes P, P. as fully'understood in the art. In the present case the. rabble mechanism (shaft` hollow arnis and rakes) is driven by a worm 4; engaging' a wormep'ear 5 on the upper end of the rahble-shaft. On the quill 6 carrying' the worm l is a sprocket 7 from which leads a chain 8 passing o-ver a sprocket T'aind operating a shaft 9 on which are disposed .sprocketwheels 10, 10'., 10, 10 of'var'ious dialneters corresponding. but set in reverse order to, a similar set of sprocket wheels l1. ll` 11, 11. on the parallel shaft l2 of the feed-screw 13 in the feed hopper lil. ,l loose chain'14 which can be shifted to any pair of sprockets drives the feed-screw. thus giving tour Speeds.A The feed can also be be started or stopped simultaneously." The clutch-shifter is not here shown as that is well understood in the art.

The present is a direct-fired furnace being provided with two diametrically opposite fire-boxes B, burning coal (though coalll/idust, oil, or gas may be substituted), each fire-box having a shaking grate Gr, an ash latmder A, and a checkerwork arch W, and discharging its gases and combustion products into the hearth c or hearth number three counting from the top. This hearth is considerably deeper than any of the remaining hearths there being left 'a clearance of from ten to twelve inches between the upper surface of the rabble-arms in said hearth and the roof of the hearth, the gases from the lire-boxes discharging into said'hearth through' the openings O which are located above the rabble arms and contiguous to the outer edge of said roof. As seenbest in Figs. l and 7, the drop holes 0 of the second hearth (b) (always counting from the top) discharge the material onto the floor of the third hearth c, the position of these particular marginal drop-holes relativelyto the discharge openings O being shown to best advantage in Fig. 7. In hearth c the roasting-ore is moving away from the circumference toward the center drop holes (special center drop holes being provided for this heart-has presently to be fully described). rlhe ore is likewise moving away from the lire-boxes, this being an important feature of my inverltion for the following reason In any direct-fired furnace used for roasting copper ore for leaching purposes, it is very important to avoid overheating any of the ore silice to do so causes a portion of the copper' contents to become insoluble in the `leaching solution, owing to the formation of ferrite coppert The temperature on the second floor or hearth Z) is by measurement approximately llOldegrees Fahr. about two feet radially from the point where the ore drops onto the third floor (c). Before the formation of insoluble copper (ferrite copper) becomes serious a temperature of at least 1100 degrees Fahr. must be exceeded, so that the quantity of insoluble copper on this floor (1)) is negligible and it makes no difference what the relative movement of theI ore and flame thereover may be. On the third floor (c) however, conditions are different. Here we have a temperature of 1280 degrees Fahr. about two feet from the furnace Walls and about midway between the drop-holes (from hearth l5) and the gas!- discharge "or fire-boxopening's O, the `telnperature being even higher closer to the said openings. The ore droppingfrom the secondl floor (Z9) has a temperature of about 500 degrees Fahr.; and were it permitted to move Vtoward thisl region or zone-of high temperature, the tendency would be for portions of the ore to become overheated and rendered insoluble as abovev pointed out. I

This overheating will obviously be much represent construction therefore, the fire-box is allowed tofdischarge into the third hearth c in which the rakes move 'the ore from the circumference toward the center. It isalso important, in order to minimize the formal' tion of insoluble or ferrite copper, and to prevent the destruction and deterioration of the rabble arms and rakes in this hearth (c) that they openings O from the fire boxes shall be immediately under the roof of the third hearth, and that this roof shall be 'so high above the rabble arms that the flame will clear the arms and play between the roof and said arms (Fig. l). It is for this reason that aclearance of from ten to twelve inches is left between the upper surface of the rabble arms and the roof of the third hearth, the rabble arms being thus brought out of range of the gases from the openings O.

In general, there are two types of roasts made use of for rendering soluble in dilute acids the copper contents of sulfid ores, towit :-(l) an oxidizing or sulfating roast, and (2). a chloridizing roast. My present furnace combines these two types, the ore being oxidized on the' three upper-"hearths or floors a, I), @,and chloridized on the three bottom floors d, e, f, the temperature of the charge being raised sufficiently high on'the oxidizing floors to permit of a rapid chloridizing action on the lower floors. The fui'- nace walls of the three bottom floors are insulated against heat loss by radiation byav layer of asbestos 19'4 or equivalent material, or by making the walls sufficiently thick to prevent loss of heat, or by means of an air space, the bottom floor being likewise properlv insulated. The insulation referred to is important since the lower floors (ai, e, f) in which the 'chloridation is taking'place are heated solely bythe heat of the calcine discharged from the upper or oxidizing hearths or floors and whichwvorksl down through said lower floors( The salt entering into the chloridizing reaction is fed to the fourth floor (il) in proper quantities through the doorsD, said salt chloridizing all the silver present (usually` a mixture of Ag, AggS, AgZSO, as a result of the oxidizing roast) as well as that portion of the copper which may have escaped conversion into oXid on the upper floors. rlhis portion is generally a copper sulfate and is converted into ehlorid as per `following reaction:-

fr portion of the copper oxid` may however.,also undergo chloridation as obvious from the following reaction t w` CuO-l--QNaCl :i CuClg-l-NagO,

the aim being to alrna'ys add sutlicient salt to chloridize` all 'the silver and that portion of the ropper not converted into oxid in the oxidizing roast. The consequence is that the composition of the final calcine which is to be leaehed, is substantially a mixture of ropper oxid, copper chlorid, `and silver chlorid, any iron present being converted into an oxid b y the heat and oxygen present, thusiocrirozreoareci.

The leaching solution employed is water containing about five per cent. by `weight of sulfuric acid and ten per cent. ,by weight of common salt, such solution readily dissolving the several components of the caleine referred to (the gangue or sand of course, being insoluble).

.ln all chloridizing roasting, a certainpercentage of the copper (usually as chlorid) volatilizes, and to save these fumes it becomes necessary to condense the same in absorption towers. In my present furnace wherein the chloridation takes place in the three lower hearths, it becomes necessary therefore to provide some means for pre-.

Venting the escape of these fumes from the chloridizing hearths (d, c, f) into the oxidizing hearths (if, c), while at the same time pern'iitting free passage of the calcine from the third (c) to the fourth (rl) hearth. lf the fumes from the lower hearths were allowed to escape to the upper hearths. they would sufl'er too great a dilution with the lire-gases, a consequence avoided herein, by the provision of specially constructed hoppers which take the placeof the central drop holes -o above referred to. vWhat would otherwise substantially correspond to a central drop hole o between the third and fourth hearths (c, el) is' closed by a sandseal 20, the seal being formed by an annular trough 21 forming the upper terminal of a sleeve vurinserted through and forming a lining for the central opening o in the lioor of the heartlirf, and a flanged disk 22 snugly passed over the .shaft l and with its flange or rim dipping under the surface of the sand in the trough and thus completing the seal. The seal 20 thus prevents escape of fumes from the fourth to the third hearth, the calcine being however free to drop from the third to the fourth hearth through the special hoppers 28, 23, disposed on the floor of the third hearth at points diametrieally opposite one another and in proximity to the sand seal 20. rlhe pas age-nay of the hopper corresponds to a section of the space between the walls of two cylinders concenseparated or spaced slightly apart. the sides of the hopper tapering downward and the bottom thereof being provided with a discharge spout 23 the outlet of which is made as small as is consistent with the free and unolistructed passage of the calcine therethrough. (Fig. 5). As just stated, the degree of separation between the opposing walls of the hopper is slight so that the caleine flowing through the hopper is practically a thin sheet or layer which, while itself freeto Apass downward and out of the outlet Q3, is fairly gas-proof so that the fumes can not readily escape through it from the fourth into the third hearth. The horizontal or cross-section of the hopper passage-way irrespective of the precise geometric curvature of its opposing walls should conform as much as possible to the cur 'ature of the arc described by the altes which in their sweep advance the ore along' radial lines at substantially uniform speed over the floor of the hearth. The hopper. therefore. if conforming in a measure to the em'vature of sucl arc will be in position to receive its charge in uniform quantities :long the full length of the curved slot forming the intake mouth or opening of the hopper passage way. The doors l) on the floors (I, c'. f (and the other floors) are made so as to lit tight. and the spare around the shaft where it passes out of the furnare through the bottom plate is made tight by the sand seal 20 (formed b V trough 2l and lianged disk 22'). The outlet. of the hopper (l which receives the caleine from' the bottom hearth (f) is constantly kept sealed by calcine. 'lhe bottom hearth is provided with a` valve-controlled opening E (see valve V on the boss ll, Fig. Q) for the admission of air to the lower three floors` the hearth l being provided with a valve-eontrolled pipe Q-t (see valve V Fig. 2) leading to any suitable exhauster or suction fan S, whereby at one operation air is drawn into the chloridixing hearths to facilitate the ehloridizing reaction, and the fumes of copper chlorid and acid gases incidental to the reaction are re- `tric with the axis of the rabble-shaft and moved, and may be properly conducted to a. suitable Aabsorption tower (not shown). Escape. efv gases through 'the openings constitut-ing the-'hoppers 23,- is prevented by maintaining la vacuum on the fourtlrfloor (d) slightly in excess of that (due to draft) on the third iioor (c), the small size of the openings especially when charged with ore; preventing mixture by eddy currents. The exhauster coupled to the pipe 24 may of course be operated so as to produce any desired pressure differential between the oxidizing and chloridizing hearths and hence maintain any degree of vacuum in the fourth hearth (eZ), the pipe 9A leading dil rectly from said hearth. The opening E and the opening for the intake end of the pipe 24 may be positioned of course where most convenient, no definite position being prescribed. therefor. By carefully regulating the valves controlling these openings any desired' quantity of air may be admitted' to, and any desired volume of fumes mayA be abstracted from, the chloridizing floors;-

the passage of gases through the openings or hopper-s 23 may also be kept at any point desired.

The ideal conditions for heating and oxidizing are a Athin bed of ore and frequent stirring; the ideal conditions on the other hand for heat conservation and chloridizing are infrequent stirring and a thick'bed of ore. Therefore, to maintain these condi` tions in the oxidizing and chloridizing regions respectively, of the furnace (hearths e, I), c, you the one hand7 and hearths el, e, f, on the other hand) two rabble arms (with a proper complement of rakes) fper floor are used in the iirst, second anti third hearths, and only one-rabble arm per Yfloor is used in the fourth, fifth and sixth hearths, the pitch and spacing of the rakes being properly adjusted to secure the necessary rotary and radial movement of the ore over the floors of the respective hearths (Fig. t).

The principal points of advantage ofthe present furnace may be summarized as follows First. The ore is about two-thirds roasted on the upper three hearths (or floors) and brought up to a good chloridizing heat by direct firing. In this way most of the sulfur is gotten rid `of without the consumption of any salt and with a much lower fuel consumption than could. be obtained in a mutlle-lired furnace. Furthermore since it is not contemplated to complet-e the roasting in the heated portions of the furnace (hearths a, o, c) there is no n eed to be over particular about the application of the flame, it being suiiicient to pass the ore quickly through a small and rather highly heated region.. i This gives a greater capacity and greater fuel economy than if a large portion of the furnace (say several iioolis)I were heated moderately. The latter principle isone on which extraneously healf ed roasting furnaces are generally built7 lthese maintaining the heat by continuous application of heat. In the present furnacethe ore is brought rapidly to a roasting temperature after which loss' of heat is prevented (in hearths d, e', f), causing the roasting to complete itself in a manner similar 'to that used for completing the cooking in a tireless cooker. Second. The ore when it drops from the third to the fourth floor is in an ideal state for chloridation with va minimum amount of salt, since it has just the correctteniperature, and, containing as it does plenty of sulfates to react with the salt, it follows that the. chlorin is freely liberated to combine with the metals of the calcine. The volatilization of copper is con fined to these (chloridizing)A floors and all of this copper can be saved in absorption towers without having to handle the gases from the fire-boxes. rfhe furnace thus possesses the goed points of a muiiie-furuace regards the handling of acid and copper fumes. Third. The reasons for combining oxidation and chloridation rather than using either alone are rma. rlhe first two-thirds say,4 of the copper is easily oxidized on direct-tired floors with no volatilization of the copper. b. The remaining one-third say, of the copper is oxidized slowly and with diliiculty, but rapidly chloridized by the addition of salt. c. Fuel consumption is less for reasons already stated; salt consumption is reduc-ed to a minimum since this Ais proportional to the sulfur present when salt is added in my furnace, the addition of the salt being made after most of the sulfur has been oxidized. lt is true that this furnace will not yield as high a proportion of watersoluble copper as a mulile furnace for sulfating or chloridizing-roasting; but thisis of little consequence in a'smelting plant treating concentrates, since acid can be made so cheaply that the saving roasting expense and salt will more than pay for it.

The waste gases from the upper three hearths escape through the uptake 25 and pipe 26. The ore traverses the several hearths under the action of the rakes, an opera-tion only too well understood in the art and there is no occasion to repeat it in the present connection.

Structural features shown but not alluded to are well known and a description thereof is here unnecessary. Qbviously, the number of hearths need not be confined to six, nor need the number of oxidizing hearths necessarily have to correspond to the number of chloridizing hearths. The-terms hearth and floor are here used indiscrimii'iately the two having substantially the same mean` ing. TWhere however the floor of 'a hearth is specifically referred to, such latter expression has reference to the bottom of the hearth in ,fcontradistinction to the roof (which forms the ioor or bottom of the neXt hearth above). Theopposingl walls of the hoppeis 23 need notof course be cylindrical; they may loe-conical or. follow the curvature of an ellipse', or the walls of a prism or pyra" mid or other shape, without departing from the spirit of my invention.

' to an oxidizing roast under direct lire in the hearths formingthel upper members of the series, the hearths forming the lower members of the series serving as chloridizing hearths, and means for maintaining 'a pressure differential between the direct-red hearth and the adjacent chloridizing hearth.

Q. In combination with a furnace havingfa sei-ies of superimposed intercommunicating hearths, means for subjecting the charge to an oxidizing; roast under direct fire, iii

` the hearths forming the upper members yot' the series, means for conserving the heat in` lierent in the charge delivered to the lower hearths whereby the `charge may be chloridized in said lower hearths wit-hout further application of heat, means for excluding any material passage of fumes from the chlorid-Y izing to the oxidizingl heart-hs, and ymeans coupled to the upper member of the chloridizing hearths, for removing the fumes from `the chloridizing hearths at a rate suiicier'ity to maintain a pressure differential between the bottom oxidizing hearth, and the adjacentA upper chlorid'izing hearth. 1

" 3. In a furnace,

ing through the hearths, hoppei's leading from the upper to the lower hearth having narrow passage-ways disposed between curved walls concentric with said axis and conforming substantially with the'curvatui'e of the arc defining the sweep of the rabble mechanism.

4. In a furnace, a pair of superimposed hearths, means for advancing the material radially toward the center, of the upper hearth, a hopper .leading from 'the upper to 'the' lower hearth and' provided with a nai'- row passage-way having a horizontal curvature concentric with the center toward which Athe material is advanced, the sides of the hopper tapering downward, and the bottom having a reduced outlet; whereby a sheet of the material fills said hopper while discharging from said reduced outlet.

In testimony whereof I affix my signature,

iii presence of two witnesses.

FREDERICK LAIST. Witnesses:

ALBERT'E. WIGGIN, WARREN JENNEY.

Copies of this patent may be obtained for ive cents each, by addressing the Commissioner'o Patents..

` Washington, D. C. I y I a'pair of superimposedA .hearths, rabble mechanism sweeping over the respective hearths from a fixed axis pass- 

